This application relates to aircraft light units, more particularly, but not exclusively, aircraft light units used when landing and/or taxiing an aircraft.
When an aircraft is landing in poor light conditions, which can be caused by poor weather and/or landing at night, it is necessary for the aircraft to illuminate the runway ahead of it in order that the pilot can land the aircraft safely. Aircraft can also vary in pitch when landing, for example, by 5 degrees or more. Therefore, the area which is it desirable to light in front of the aircraft changes position in respect to the aircraft.
Existing aircraft light units comprise filament based tungsten lamps situated at the bottom front end of the aircraft which are activated when the aircraft begins the landing approach. Once the aircraft has landed it may also be necessary to illuminate the runway when taxiing off the landing strip and filament based tungsten lamps are used again. They may be activated separately, or together with the landing light units.
Filament based tungsten lamps are inefficient and produce a large amount of heat during use. Filament based tungsten lamps typically have a broad distribution of intensity, meaning that as the aircraft is landing, only a small amount of the total light output illuminates the intended area.
Furthermore, due to aircraft vibration, filament based tungsten lamps have a short lifespan, needing, for example, replacement after between 30 and 100 hours of use. This leads to the aircraft requiring an increased amount of maintenance and increasing the aircraft running costs. Also, due to the high failure rate, a high level of redundancy is built into the lighting systems of an aircraft, increasing the aircraft weight.
A further factor which increases the weight of an aircraft is the fact that as an aircraft comes into land, the aircraft's pitch attitude, altitude and velocity relative to the ground varies. As a result, the area of runway that needs to be illuminated changes. In order to light these areas satisfactorily, it may be necessary to have a plurality of light units on an aircraft, each arranged to light a different area relative to the aircraft, thereby compensating for the change of aircraft position and velocity with respect to the ground. The greater the number of light units, the larger the weight of the aircraft, which has well known disadvantages for aircraft.
Certain aircraft light units have been provided with motors to actuate the light unit between different lighting positions, for example, see U.S. Pat. No. 5,355,131 (Metz et al). However, the addition of the motor adds both weight and complexity to the aircraft light unit.
The present invention seeks to mitigate or overcome one or more of the above-identified disadvantages associated with the prior art.